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<H1>IBM Visualization Data Explorer Programmer&#39;s Reference</H1>
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<HR>
<H2><A NAME="Header_161" HREF="progu075.htm#PToC_161">16.3 Tiling</A></H2>
<A NAME="IDX1233"></A>
<A NAME="IDX1234"></A>
<P>
Tiling is the process of combining shaded surface and volume
interpolation elements to produce an image.
The following table lists elements that are defined and implemented
("yes").
A dash identifies a meaningless combination.
<BR>
<TABLE BORDER>
<TR>
<TH ALIGN="LEFT" VALIGN="TOP" WIDTH="33%">Component
</TH><TH ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">irregular
</TH><TH ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">regular
</TH><TH ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">opaque
</TH><TH ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">translucent
</TH></TR><TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="33%">"lines"
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD></TR><TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="33%">"triangles"
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">--
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD></TR><TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="33%">"quads"
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD></TR><TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="33%">"tetrahedra"
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">--
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">--
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD></TR><TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="33%">"cubes"
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">--
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD></TR><TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="33%">"faces," "loops," "edges"
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">--
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="17%">yes
</TD></TR></TABLE>
<P>
Lines may be irregular unconnected vectors or <I>paths</I> having
regular 1-dimensional connections.
Surfaces and volumes may be (1) completely irregular, (2) regular in
connections but irregular in positions, or (3) regular in both
connections and positions (<A HREF="#FIGAO6AFG3">Figure 11</A>).
<P>
<P><B><A NAME="FIGAO6AFG3" HREF="../proguide.htm#FT_FIGAO6AFG3">Figure 11. Types of
Connections and Positions</A></B><BR>
<B><BR><CENTER><IMG SRC="../images/gridtype.gif" ALT="Figure gridtype not
displayed."></CENTER><BR></B><BR>
<P>
<H3><A NAME="HDRRENDMDL" HREF="progu075.htm#PToC_162">Rendering Model</A></H3>
<A NAME="IDX1235"></A>
<A NAME="IDX1236"></A>
<P>
The interpretation of "colors" and "opacities" differs
between surfaces and volumes.
For surfaces, a surface of color <I>c<SUB>f</SUB></I> and opacity <I>o</I>
are combined with the color <I>c<SUB>b</SUB></I> of the objects behind it,
resulting in a combined color
<I>c<SUB>f</SUB>o&nbsp;&#43;&nbsp;c<SUB>b</SUB>&nbsp;(1&nbsp;&#45;&nbsp;o)</I>.
<P>
For volumes, the "dense emitter" model is used, in which the
opacity represents the instantaneous rate of absorption of
light passing through the volume per unit thickness,
and the color represents the instantaneous rate
of light emission per unit thickness.
If <I>c(z)</I> represents the color of the object at
<I>z</I> and <I>o(z)</I> represents its
opacity at <I>z</I>, the total color <I>c</I>
of a ray passing through the volume is given by:
c % = % integral to infinity from &lt; - infinity &gt; % c ( z ) % 'exp' %
left lparen minus integral to &lt; z &gt; from &lt; - infinity &gt; % o ( zeta )
d
zeta right rparen % dz
<P>
<H3><A NAME="Header_163" HREF="progu075.htm#PToC_163">Tiling Options</A></H3>
<A NAME="IDX1237"></A>
<P>
Tiling options are controlled by a set of Object
attributes.
These attributes may be associated with Objects at any level of a
Field/Group hierarchy.
The attributes may be set by using the
<TT><STRONG>DXSetAttribute()</STRONG></TT>
function, or by using the Options
module.
The attributes are:
<BR>
<TABLE BORDER>
<TR>
<TH ALIGN="LEFT" VALIGN="TOP" WIDTH="50%">Attribute
</TH><TH ALIGN="LEFT" VALIGN="TOP" WIDTH="50%">Meaning
</TH></TR><TR>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH="50%">"fuzz"
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="50%">object fuzz
</TD></TR></TABLE>
<A NAME="IDX1238"></A>
<A NAME="IDX1239"></A>
<P>
<I>Object fuzz</I> is a method of resolving conflicts between
objects at the same distance from the camera.
For example, it may be desirable to define a set of lines coincident
with a plane.
Normally it will be unclear which object is to be displayed
in front.
In addition, single-pixel lines are inherently inaccurate (i.e. they
deviate from the actual geometric line) by as much as one-half
pixel;
when displayed against a sloping surface, this <I>x</I> or
<I>y</I> inaccuracy is equivalent to a <I>z</I>
inaccuracy related to the slope of the surface.
The "fuzz" attribute specifies a <I>z</I> value that will be
added to the object before it is compared with other objects in
the scene, thus resolving this problem.
The fuzz value is specified in pixels.
For example, a fuzz value of one pixel can compensate for the
described half-pixel inaccuracy when the line is displayed
against a surface with a slope of two.
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